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Clues to language origins seen in ape gestures

April 30, 2007
Courtesy PNAS
and World Science staff

Sci­en­tists have found what they call new ev­i­dence for a the­ory that lan­guage be­gan with ges­tures. Chim­p­an­zees and their close rel­a­tives use ges­tures more flex­i­bly than fa­cial ex­pres­sions and sounds to com­mu­ni­cate, the re­search­ers say.

Amy Pol­lick and Frans de Waal at the Yer­kes Na­tion­al Pri­mate Re­search Cen­ter of Em­o­ry Uni­ver­si­ty in At­lan­ta, worked with two groups each of two close hu­man rel­a­tives, chimps and bono­bos, 47 an­i­mals in all.

The bonobo, Pan panis­cus, un­til re­cent­ly called pyg­my chim­pan­zee. They are close rel­a­tives of chimps, be­lieved to have branched off the chimp line­age af­ter that line­age split off from hu­man an­ces­tors. (Im­age cour­te­sy Wa­rimo)
The pair dis­tin­guished 31 man­u­al ges­tures and 18 fa­cial or vo­cal sig­nals. They al­so found si­m­i­lar use of fa­cial and vo­cal sig­nals, but not of the ges­tures, be­t­ween the spe­cies. 

Man­u­al ges­tures were less close­ly tied to par­tic­u­lar emo­tions and, there­by, were more adapt­a­ble, the in­ves­ti­ga­tors said. A ges­ture may com­mu­ni­cate a to­tal­ly dif­fer­ent mes­sage de­pend­ing up­on the con­text, they added.

“A chim­pan­zee may stretch out an open hand to an­oth­er as a sig­nal for sup­port, where­as the same ges­ture to­ward a pos­ses­sor of food sig­nals a de­sire to share,” said Pol­lick. 

“A scream, how­ev­er, is a typ­i­cal re­s­ponse for vic­tims of in­tim­i­da­tion, threat or at­tack. This is so for both bo­no­bos and chim­pan­zees, and sug­gests the vo­ca­l­i­z­a­tion is rel­a­tively in­va­ri­ant.”

By stu­dy­ing si­m­i­lar types of com­mu­ni­ca­tion in close­ly re­lat­ed spe­cies, re­search­ers can make de­duc­tions about shared an­ces­try. We know ges­tures are a more re­cent ev­o­lu­tion­ary de­vel­op­ment than fa­cial ex­pres­sions and vo­calizations, Pol­lick and de Waal said, be­cause apes and hu­mans ges­tic­u­late—but not mon­keys, a more an­cient line­age.

“A ges­ture that oc­curs in bono­bos and chim­pan­zees as well as hu­mans like­ly was pre­s­ent in the last com­mon an­ces­tor” of all three, said Pol­lick. “A good ex­am­ple of a shared ges­ture is the open-hand beg­ging ges­ture, used by both apes and hu­mans. This ges­ture can be used for food, if there is food around, but it al­so can be used to beg for help, for sup­port, for mon­ey and so on. Its mean­ing is con­text-dependent,” added de Waal. 

The re­search­ers al­so found bono­bos use ges­tures more flex­i­bly than do chim­pan­zees. “D­if­fer­ent groups of bono­bos used ges­tures in spe­cif­ic con­texts less con­sist­ent­ly than did dif­fer­ent groups of chim­pan­zees,” said Pol­lick. The re­searchers’ find­ings al­so sug­gest bo­no­bos and chim­pan­zees en­gage in multi-modal com­mu­ni­ca­tion, com­bin­ing their ges­tures with fa­cial ex­pres­sions and vo­calizations to com­mu­ni­cate a mes­sage, they added. “While chim­pan­zees pro­duce more of these com­bi­na­tions, bono­bos re­spond to them more of­ten. This find­ing sug­gests the bonobo is a bet­ter mod­el of sym­bol­ic com­mu­ni­ca­tion in our ear­ly an­ces­tors,” con­clud­ed Pol­lick.

This study ap­pears in the on­line ear­ly edi­tion of the re­search jour­nal Pro­ceed­ings of the Na­tion­al Acad­e­my of Sci­ences this week.

The idea that lan­guage arose from ges­tures dates back to the 18th cen­tu­ry and draws sup­port from sev­er­al mod­ern lines of ev­i­dence, sci­ent­ists say. These include the neu­rol­o­gy of lan­guage; the com­p­lex­ity and cross-cultural na­ture of sign lan­guages; and apes’ abi­li­ties to learn sign language.



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Homepage image: bonobo, courtesy MPI-EVA; © Science

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Scientists have found what they call new evidence that language began with gestures. Chimpanzees and their close relatives use gestures more flexibly than facial expressions and sounds to com municate, the researchers say. Amy Pollick and Frans de Waal at the Yerkes National Primate Research Center of Emory University in Atlanta, worked with two groups each of two close human relatives, chimps and bonobos, 47 animals in all. The pair distinguished 31 manual gestures and 18 facial or vocal signals. They also found similar use of facial and vocal signals, but not of the gestures, between the species. Manual gestures were less closely tied to particular emotions and, thereby, were more adaptable, the invest igators said. A gesture may com municate a totally different message depending upon the context, they added. “A chimpanzee may stretch out an open hand to another as a signal for support, whereas the same gesture toward a possessor of food signals a desire to share,” said Pollick. “A scream, however, is a typical response for victims of intimidation, threat or attack. This is so for both bonobos and chimpanzees, and suggests the vocalization is relatively invariant.” By studying similar types of com munication in closely related species, researchers can make deductions about shared ancestry. We know gestures are a more recent evolution ary development than facial expressions and vocalizations, Pollick and de Waal said, because apes and humans gesticulate—but not monkeys, a more ancient lineage. “A gesture that occurs in bonobos and chimpanzees as well as humans likely was present in the last common ancestor,” said Pollick. “A good example of a shared gesture is the open-hand begging gesture, used by both apes and humans. This gesture can be used for food, if there is food around, but it also can be used to beg for help, for support, for money and so on. It’s meaning is context-dependent,” added de Waal. The researchers also found bonobos use gestures more flexibly than do chimpanzees. “Different groups of bonobos used gestures in specific contexts less consistently than did different groups of chimpanzees,” said Pollick. The researcher’s findings also suggest bonobos and chimpanzees engage in multi-modal com munication, combining their gestures with facial expressions and vocalizations to com municate a message, they added. “While chimpanzees produce more of these combinations, bonobos respond to them more often. This finding suggests the bonobo is a better model of symbolic com munication in our early ancestors,” concluded Pollick. This study appears in the online early edition of the research journal Proceedings of the National Academy of Sciences this week.